DE102007002809A1 - Method for pulsed operation of lighting unit with light emitting diodes for motor vehicles, involves dephasing of pulse mode of two light-emitting diodes of two groups - Google Patents

Abstract

The method involves dephasing of a pulse mode of two light-emitting diodes of two groups such that a switch-on time of the light emitting diode or the group of light emitting diodes partly fall in the phase of other light emitting diode or group of light emitting diodes. The switch-on time of the light emitting diode or group of light emitting diodes begins, when the switch-on time of other light emitting diode or group of light emitting diodes ends.

Description

The The invention relates to a method for operating a lighting device (Taillights or headlamps) for motor vehicles, wherein the illumination device one or more light emitting diodes (LEDs) includes.

Especially because of the longer life is now the use of LEDs instead of incandescent bulbs in vehicle tail lights since then widespread some time ago. Here are the various tail light functions (Brake light, tail light, flashing light) using realized by LEDs. Beyond that, already for the realization of front light functions in headlamps (eg Position light and daytime running light) LEDs are used. Future also Ablend- and high-beam functions are realized with LEDs become.

The LEDs are operated pulsed for a variety of reasons. So it is for example from the documents DE 10 2004 036 137 A1 . DE 199 45 546 A1 and DE 10027 478 A1 It is known to realize various light functions (eg brake light and tail light) with a single LED illumination device by dimming via a so-called pulse width modulation (PWM). By modulating the pulse width ratio (ratio of switch-on time to period T: also called the duty cycle), the average current or power consumption of the LEDs and thus the luminous flux of the respectively desired light function can be adjusted.

In addition, it is also known (see DE 103 24 609 A1 ), to use the method of PWM dimming in LED lighting equipment to keep the brightness and the color of the LEDs constant even with surges due to vehicle electrical system fluctuations or thermal loads.

Since LEDs (semiconductor light sources), in contrast to incandescent lamps, reach their desired intensity immediately after switching on and are dark immediately after switching off, a pulsed LED illumination device can quickly give the viewer the impression of a flickering light. To avoid this, in the prior art (see DE 10 2004 003 844 A1 and DE 199 33 733 A1 ) proposed to operate pulsed LED lighting devices with a high frequency (50 Hz or higher), since then the impression of a permanent light arises for the human eye. It is claimed in the prior art that at frequencies of 50 Hz or higher no stroboscopic effect occurs anymore. This is not true. Observations have rather shown that even with a pulsed with 100 Hz LED tail light (eg tail light) a disturbing flicker due to the pulse operation is perceived, and that is when the LED lighting device or the illuminated by this objects with relative high angular velocity to the viewer move. Relatively high angular velocities of this kind are also given, in particular, when looking at the eye. Insiders had the considerations in the prior art for flickering in pulse mode not actually related to the stroboscopic effect, since in the prior art, the relative movement between the viewer and LED lighting device or illuminated objects was not considered.

Indeed is for the viewer with a pulsed operation of 100 Hz no flicker more perceptible when the LED lighting device or her reflection static at a constant angle be, since the human eye in this case the dark phases can not resolve in time.

If the LED lighting device or its reflection, however be considered at a high angular velocity is for the viewer despite a pulse rate of 100 Hz due to the Stroboscopic effect a disturbing flicker noticeable.

task The invention is therefore a method for pulsed operation of LED lighting devices for motor vehicles too create, with which the disturbing stroboscopic effect is effective reduced or avoided.

to Solution to this problem is proposed according to the invention, that the pulse operation of at least two LEDs or at least two Light-emitting diode groups out of phase so that the turn-on a light emitting diode or light emitting diode group at least partially in the switch-off time of another LED or light-emitting diode group lies. In this way, for the perception of the Stroboscopic effect reduced crucial duration of the dark phase or even eliminated.

As a further solution, the invention proposes to change the pulse width ratio (ratio of switch-on time to period T) and the magnitude of the current pulse (I _pulse ) as a function of the vehicle speed, wherein the pulse width ratio increases with increasing speed, while the magnitude of the current pulse (I _pulse ) decreases with increasing speed. At the same time it is ensured that the integral averaged desired luminous flux is achieved. At higher vehicle speeds, where the stroboscopic effect is more noticeable, the magnitude of the current pulse (I _pulse ) will increase in favor of a longer one reduced switching time, whereby the dark phase is shortened in an advantageous manner. It can happen that one comes in reducing the height of the current pulses (I _pulse ) in a lower current range, where the relationship between current and light intensity is no longer equally stable and reproducible for all LEDs. In an arrangement of a plurality of LEDs, it may then happen that the individual LEDs have a slightly different brightness and possibly a slight color shift among each other. This phenomenon, also referred to as "mottling", which is undesirable for decorative and functional reasons, is perceived as less disturbing than the stroboscopic effect at high speeds, but at low driving speeds the stroboscopic effect is less pronounced the current pulses (I _pulse ) is increased at the expense of the turn-on time in order to avoid a "blotchy" appearance of the LEDs in the LED illumination device.

Furthermore, the invention proposes that the current flow takes place with a periodically modulated current signal, wherein the current flow within the period (T) during a first time interval (T _High ) with a current (I _High ), which is higher than the current (I _Low ) during the remainder of the time (T _Low = T - T _High ), where the current (I _Low ) is greater than zero. This realizes a quasi-pulsed operation. Quasi therefore, because even in the actual dark phase, the at least one LED with a - albeit small - applied to non-zero current and thus excited to shine. This avoids an absolute darkness in the "off-time", and some "blotchiness" due to the low current in the "dark phase" is accepted, reducing the brightness contrast between the phases and reducing the perceptibility of the stroboscopic effect.

Based In the accompanying drawings, the invention will be described below explained in more detail.

there shows:

1 a schematic representation for the perception of the contrast of an LED illumination device to illustrate the stroboscopic effect,

2 a representation like in 1 for two different viewing angles,

3 a first time diagram for the phase-shifted operation of two LEDs or LED groups,

4 a second time diagram for the phase-shifted operation of two LEDs or LED groups,

5 a time diagram for the phase-shifted operation of three LED groups,

6 a circuit arrangement for the phase-shifted operation of three LED groups,

7 a timing diagram for the quasi-pulsed operation of a LED lighting device.

1 shows a schematic representation for the perception of the contrast of an LED lighting device to illustrate the stroboscopic effect. The pulse-operated LED illumination device is, for example, an LED headlamp whose reflection, reflected by, for example, lateral guide posts, is observed by the eye of an observer. With a pulse frequency f of the LED illumination device, a pulse width ratio n (ratio of the switch-on time to the period T = 1 / f) and a vehicle speed v of the vehicle on which the LED illumination device is arranged, determines the dark path length L _D , ie the length of the distance traveled during the dark phase, to: L _D = v × (1-n) / f.

At a pulse frequency of f = 100 Hz, a pulse width ratio of n = 10% and a vehicle speed of v = 100 km / h results in a dark path length of L _D = 25 cm. When viewing objects or their reflection on the roadside, z. However, for example, delineators or trees detected at a viewing angle (α) will reveal the portion of the dark zone which is imaged in a spatially resolved manner on the retina of the eye. This causes the perceived annoying stroboscopic effect.

ever greater the lateral viewing angle (α) is, the greater is the one for the Illustration of the dark zone on the retina crucial dark angles (Β).

A

den Abstand der gepulst beleuchteten Objekte vom Auge des Betrachters,

D

den seitlichen Abstand der Objekte vom Auge des Betrachters,

α

den Betrachtungswinkel,

n

das Pulsweitenverhältnis,

R

die Entfernung zum Objekt,

L_D

Länge der Dunkelzone,

L_d

den ortsaufgelösten Teil der Dunkelzone, der unter dem Blickwinkel (α) wahr genommen wird,

v

Relativgeschwindigekeit zwischen dem Betrachter und dem leuchtendem/beleuchteten Objekt,

This will be explained below with reference to 2 be explained. Where:

A

the distance of the pulsed illuminated objects from the eye of the observer,

D

the lateral distance of the objects from the eye of the observer,

α

the viewing angle,

n

the pulse width ratio,

R

the distance to the object,

L _D

Length of the dark zone,

L _d

the spatially resolved part of the dark zone, which is perceived from the point of view (α),

v

Relative speed between the viewer and the illuminated / illuminated object,

The following relationships apply:
α = arctane (D / A)
L _d = L _D × sin α
R = D / sinα
β = arcsin (L _d / R)

The dark angle (β), which is decisive for the imaging of the dark zone on the retina, is calculated as an approximation for the relevant region (α> 45 ^° ) from this as follows: β = arcsin {V × sin 2 α × (1-n) / (f × D)}

If the dark angle (β) is greater than the physiological one effective angular resolution of the eye, which is not continuous Illumination of objects visible due to the stroboscopic effect.

The perceptibility of the stroboscopic effect is greatest for objects near the roadside (α -> 90 ⁰ ); it increases with increasing vehicle speed and decreasing pulse width ratio and decreases with higher frequency.

In In driving practice, this means that objects at the edge of the road at Driving past show a particularly strong stroboscopic effect, so For example, guide posts, trees, but especially strong reflective objects such as lane markings and traffic signs.

For the road users, this means that the stroboscopic effect Objectively pronounced in the zone of the visual field edge is where he is because of the physiologically pronounced sensibility too subjectively is particularly intense. Consequently, the stroboscopic effect as a latently elevated, subliminal stress factor extremely disturbing and the traffic safety by a faster Fatigue at night driving adversely affect. Of the Stroboscopic effect is accordingly perceived when cornering.

one Reduction of the stroboscopic effect by increasing the Pulse frequency are limited. On the one hand then the thermal power losses in the control unit for controlling the LED lighting device increased, on the other hand is a frequency increase also adversely with an increase in electromagnetic Interference radiation connected.

According to the stroboscopic effect is reduced by the fact that the pulse operation of at least two light-emitting diodes or at least two light-emitting diode groups within the LED lighting device is carried out in phase such that the turn-on of a light emitting diode or light emitting diode group is at least partially in the off time of another light emitting diode or light emitting diode group. An example of this is in 3 shown. The two LEDs or LED groups are operated with a pulse frequency of 100 Hz and a pulse width ratio of 50%, so that the switch-on time and the switch-off time are each 5 ms. According to the invention, the two LEDs or LED groups are now controlled in a phase-shifted manner so that the switch-on time of one LED / LED group lies precisely in the switch-off time of the other LED / LED group. The phase shift is therefore in this example at a pulse width ratio of 50% exactly half a period (T / 2). In this way, there is no dark phase and thus also a dark path length more, so that the stroboscopic effect is completely avoided. If the one LED or LED group is turned on exactly when another one is turned off and vice versa, the total current for the LED lighting device flows more uniformly overall, thereby advantageously avoiding or reducing electromagnetic interference radiation as well.

When separately controllable light-emitting diode group can be a series or parallel connection be used by two or more light-emitting diodes. It can, however also a parallel connection of two or more LED series circuits be used as a separately controllable light emitting diode group. About that In addition, an LED matrix circuit consisting of a plurality of light-emitting diodes can be used as a separately controllable light-emitting diode group, when the LEDs in a combined parallel / series circuit are arranged.

4 shows another example of the phase-shifted operation of at least two light emitting diodes or at least two light emitting diode groups within the LED lighting device. The two LEDs or LED groups are operated with a pulse frequency of 100 Hz and a pulse width ratio of 30%, so that the switch-on time is 3 ms and the switch-off time is 7 ms. Erfindungsge according to the two LEDs or LED groups are now so out of phase angesteu ert that the turn-on of the one LED / LED group is in the off time of the other LED / LED group, preferably centered. In this way, the dark phase is reduced from 7 ms to two very short dark phases of 2 ms each.

5 shows an example of the inventive control of an LED brake / tail light. In this case, a single LED arrangement consisting of a plurality of LEDs is used to realize both the brake light and the tail light function. In this case, a ratio of about 10: 1 prescribed for the ratio of the light intensity of brake light to tail light, ie, the brake light is 10 times as bright as the tail light. To realize the brake light is - as long as the brake signal is applied to the LED lighting device with a continuous current (I ₀ ) applied, ie from the perspective of PWM modulation, the pulse width ratio is then 100%. To realize the tail light function is then carried out a PWM dimming. The upper time diagram shows the 5 the procedure of the prior art. According to the prior art, the tail light function is effected by a PWM dimming with a pulse width ratio of 10%, ie at a pulse frequency of 100 Hz (period T = 10 ms), the turn-on time is 1 ms. However, the pulsed LED lighting device generates the disturbing stroboscopic effect described above.

According to the invention, the LEDs of the LED illumination device are now divided into N separately controllable LED groups. In the embodiment according to the 5 and 6 3 LED groups are provided. To realize the tail light, the pulsed current (I _pulse ) is applied to the LED groups, the pulse width ratio (ratio of on-time to period T) being 1 / N, with the individual light-emitting diode groups successively switching on and off with a phase shift of T / N turned off. In this way, the dark phases are completely avoided. In order to reduce the taillight function the light intensity with respect to the brake light function by a factor of about 10, a lowering of the Pulstroms to (I _0/3) is also provided in addition to a pulse width ratio of 1/3. When the current is reduced to one third of the value for the brake light function, there is still no "blotchy" appearance of the LED arrangement.A reduction of the pulse current for realizing the tail light function can be dispensed with if 10 separately controllable LEDs or LED groups are used in which the individual LEDs or LED groups are switched on and off sequentially with a phase shift of T / 10.

A circuit arrangement for the phase-shifted operation of three LED groups is in 6 shown. The LED array consists of a total of 18 LEDs (D1 to D18), which in turn are divided into 6 LED series circuits, each LED series circuit is a series resistor (R1 to R6) is switched on. To realize a PWM operation, three switches (S) are provided with which the LED current can be switched on and off by individual LED groups. In this case, the first and the fourth LED series circuit to a via a switch (S) separately controllable 1st LED group summarized (Note: The numbering of the LED series connections refers to the numbering of the series resistors). In addition, the 2nd and the 5th LED series circuit to a 2nd LED group and the 3rd and the 6th LED series circuit to a 3rd LED group are summarized. The invention phase-shifted control of the individual switches via a control unit.

It is particularly advantageous if the light-emitting diodes of at least two mutually phase-shifted operated LED groups are arranged spatially interleaved with each other (see 6 ). Here, a part of the LEDs (D4 to D6) of the 2nd LED group and a part of the LEDs (D7 to D9) of the 3rd LED group spatially from the light emitting diodes (D1 to D3, D10 to D12) of the 1st LED Group bordered. This interlacing continues accordingly, with a portion of the LEDs (D7 to D9) of the 3rd LED group and a portion of the LEDs (D10 to D12) of the 1st LED group spatially separated from the LEDs (D4 to D6, D13 to D15) of the second LED group. In addition, a part of the light emitting diodes (D10 to D12) of the 1st LED group and a part of the light emitting diodes (D13 to D15) of the 2nd LED group spatially from the light emitting diodes (D7 to D9, D16 to D18) of the 3rd LED Group bordered.

at this type of nesting in conjunction with the phase-shifted PWM control is a largely homogeneous luminance distribution over reaches the entire light area of the LED array. By this type of nesting becomes a streaky appearance that can occur when viewed from close proximity, strong reduced.

7 shows a timing diagram for the quasi-pulsed operation of an LED lighting device. During quasi-pulsed operation, the at least one LED is also subjected to a current I _Low, which is different from zero, even in the actual dark phase, and is therefore excited to glow. This avoids an absolute darkness in the "off-time", a certain "blotchiness" due to the low current in the "dark phase" is thereby accepted in the resulting reduction in brightness cont between phases, the perception of the stroboscopic effect is also reduced.

In In another embodiment, it is provided, the pulse rate speed-dependent, the frequency is increased with increasing travel speed. By the increase in the pulse rate, as already mentioned above, the dark path length is also reduced, so by that the greater perceptibility of the stroboscopic effect is compensated at higher travel speeds. A Although increased pulse rate also leads to a increased power loss of the electronic control device for the LED light source, but especially for LED headlamps not so problematic, because the frequency and thus the power dissipation yes only increased if more intensive cooling is available through the wind.

The speed-dependent adjustment of the pulse rate can be considered as a sole measure or beneficial in Connection with the phase-shifted operation can be used.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 102004036137 A1 [0003]
• - DE 19945546 A1 [0003]
• - DE 10027478 A1 [0003]
• - DE 10324609 A1 [0004]
• - DE 102004003844 A1 [0005]
• - DE 19933733 A1 [0005]

Claims (12)

Method for the pulsed operation of a lighting device with light-emitting diodes (LED) for motor vehicles, characterized in that the pulse operation of at least two light-emitting diodes or of at least two light-emitting diode groups out of phase so that the turn-on of a light emitting diode or light emitting diode group at least partially in the off time of another light emitting diode or light emitting diode group lies. Method according to claim 1, characterized in that that the turn-on time of a light-emitting diode or light-emitting diode group begins when the turn-on time of another LED or light-emitting diode group ends. Method according to claim 1, characterized in that that the switch-on time of a light-emitting diode or light-emitting diode group, preferably in the middle in the off time of another LED or light-emitting diode group is located. Method according to one of the preceding claims, characterized in that as separately controllable light-emitting diode group a series connection of two or more light-emitting diodes is used. Method according to one of the preceding claims, characterized in that as separately controllable light-emitting diode group a parallel connection of two or more light emitting diodes used becomes. Method according to one of the preceding claims, characterized in that as separately controllable light-emitting diode group a parallel connection of two or more LED series circuits is used. Method according to one of the preceding claims, characterized in that as separately controllable light-emitting diode group an LED matrix circuit consisting of a plurality of light-emitting diodes is used. Method according to one of the preceding claims, characterized in that the light-emitting diodes of at least two mutually phase-shifted operated light emitting diode groups with each other spatially nested are arranged. Method according to one of the preceding claims, characterized in that - the LED illumination device is used both as a tail light and as a brake light, - the LED illumination device N (= 3 or more) has separately controllable light-emitting diodes or light-emitting diode groups, - the light-emitting diodes or light-emitting diode groups the LED lighting device in the use as a brake light with a non-pulsed current of height (I ₀ ) are applied, - the LEDs or light emitting diode groups of the LED lighting device in the use as a tail light with a pulsed current (I _pulse ) are applied, the Pulse width ratio (ratio of on-time to period T) 1 / N, with the individual light-emitting diodes or LED groups successively switched on and off with a phase shift of T / N. A method according to claim 9, characterized in that the height of the pulsed current (I _pulse ) when used as a tail light is smaller than the height of the non-pulsed current (I ₀ ) when used as a brake light. Method for the pulsed energization of a lighting device with at least one light emitting diode (LED) for motor vehicles, characterized in that the pulse width ratio (ratio of turn-on time to period T) and the height of the current pulse (I _pulse ) are changed depending on the vehicle speed, wherein the pulse width ratio with Increasing speed increases, while the height of the current pulse (I _pulse ) decreases with increasing speed. A method for energizing a lighting device with at least one light emitting diode (LED) for motor vehicles, characterized in that the energization is carried out with a periodically modulated current signal, the energization within the period (T) during a first time interval (T _High ) with a current (I _High ), which is higher than the current (I _Low ) during the remaining period (T _Low = T - T _High ), wherein the current (I _Low ) is greater than zero.